Adsorptive monolith including activated carbon, method for making said monolith, and method for adsorbing chemical agents from fluid streams

ABSTRACT

An adsorptive monolith made by extruding a mixture of activated carbon, a ceramic forming material, a flux material, and water, drying the extruded monolith, and firing the dried monolith at a temperature and for a time period sufficient to react the ceramic material together and form a ceramic matrix. The extrudable mixture may also comprise a wet binder. The monolith has a shape with at least one passage therethrough and desirably has a plurality of passages therethrough to form a honeycomb. The monolith may be dried by vacuum drying, freeze drying, or control humidity drying. The monolith is useful for removing volatile organic compounds and other chemical agents such as ozone from fluid streams. Particularly useful applications include adsorptive filters for removing ozone from xerographic devices and other appropriate office machines and volatile organic compounds from automobile engine air intake systems.

This application is a continuation of application Ser. No. 09/267,119filed Mar. 10, 1999, now abandoned, which is a divisional application ofapplication Ser. No. 08/636,700, filed Apr. 23, 1996 now U.S. Pat. No.5,914,294 issued June 22, 1999.

TECHNICAL FIELD

This invention relates to adsorptive monoliths including activatedcarbon and more particularly to adsorptive monoliths including ceramicmaterial and activated carbon and using said monolith to remove volatileorganic compounds, ozone, and other chemical agents from fluid streams.

BACKGROUND OF THE INVENTION

Activated carbon is useful in the removal of chemical agents such asvolatile organic compounds from fluid streams and is also useful as acatalyst substrate for special applications. To remove chemical agentsfrom a fluid stream with activated carbon, the fluid stream is directedadjacent the activated carbon. The activated carbon can be in the formof particles in a packed column, a coating on a substrate, a monolithwith passages for fluid flow therethrough, and the like.

It is desirable in some activated carbon applications to have a highrate of fluid flow adjacent to the activated carbon and a low level ofback pressure. Thus, packed columns of activated carbon are sometimesunsuitable because of the high level of back pressure created. Formedbodies containing activated carbon and having open passagestherethrough, such as a honeycomb-shaped activated carbon monolith, aredesirable for applications wherein a reasonably high rate of fluid flowand a low level of back pressure are required, but formation of suchshapes with a level of strength sufficient to withstand handling and useas an adsorbent filter is problematic. Activated carbon monoliths formedwithout a binder do not have sufficient strength for some applications.

U.S. Pat. No. 4,518,704 to Okabayashi et al. discloses a formed bodycomprising activated carbon and a ceramic material. This structure hasimproved strength properties but Okabayashi teaches firing at atemperature of 1100° C. for a period from 1 to 4 hours to achievedesired bonding and strength. Firing at such a high temperature and forsuch a long period of time is economically undesirable.

Another problem with making adsorptive monoliths comprising activatedcarbon and a ceramic material is that it is difficult to extrude amixture of activated carbon and ceramic forming material without a highlevel of water in the mixture due to the high porosity of the activatedcarbon. To successfully extrude a mixture of activated carbon andceramic forming material into a shape such as a honeycomb, a watercontent of 30 to 65 percent by weight is required. This moisture must besubstantially removed from the extruded monolith before firing toprotect the integrity of the formed monolith. A ceramic articlesubjected to increased temperature during firing, without first havingbeen relieved of most of its moisture content, will usually suffersignificant damage in the form of cracks, pop-outs or explosions due torapid conversions of its remaining moisture to steam.

Drying of a wet, extruded monolith of ceramic forming material andactivated carbon is a sensitive process. An unfired ceramic productgenerally shrinks as it loses moisture, and a monolith can crack if therate of moisture loss from the monolith during drying is not uniformthroughout the monolith.

Accordingly, there is a need for a formed body comprising activatedcarbon that can be formed by extrusion, can be dried and fired withoutcracking, can be fired at more economical conditions such as a lowertemperature and a shorter time, has sufficient strength to withstandhandling and use as an adsorptive filter, and has a shape whichaccommodates sufficient fluid flow throughput.

SUMMARY OF THE INVENTION

This invention solves the above-described problems by providing a methodof forming an adsorptive monolith comprising extruding an extrudablemixture including an activated carbon, a ceramic forming material,water, and a flux material. The flux material enhances the fusing of theceramic forming material upon firing by lowering the temperature atwhich the ceramic forming material fuses and forms ceramic bonds. Thisallows the monolith to be fired at a lower temperature and for a shortertime. In addition, the invention encompasses methods of drying the wetextruded monolith including vacuum drying, freeze drying, and humiditycontrol drying. Such drying methods allow the wet extruded monolith tobe dried without cracking of the monolith.

More particularly, this invention encompasses a method of forming anadsorptive monolith comprising the steps of (a) extruding an extrudablemixture through an extrusion die such that a monolith is formed having ashape wherein the monolith has at least one passage therethrough and theextrudable mixture comprises activated carbon, a ceramic formingmaterial, a flux material, and water, (b) drying the extruded monolith,and (c) firing the dried monolith at a temperature and for a time periodsufficient to react the ceramic forming material together and form aceramic matrix. The extrudable mixture is capable of maintaining theshape of the monolith after extrusion and during drying of the monolith.

A suitable ceramic forming material is ball clay. In addition, theceramic forming material desirably includes a filler for reducingshrinkage of the monolith during the steps of drying and firing. Asuitable filler is calcined kaolin clay.

A suitable flux material is a feldspathic material, particularly,nepheline syenite.

Desirably, the extrudable mixture includes a wet binder for enhancingstrength and maintaining the shape of the wet extruded monolith. Aparticularly suitable wet binder is methylcellulose. Acrylic binders arealso suitable and can be used in combination with methylcellulose.

The extrudable mixture can also include sodium silicate which, as abinder, enhances the strength of the monolith during drying and, as aflux material, enhances the strength of the monolith after firing.

Desirably, the adsorptive monolith has a plurality of passagestherethrough and is in the shape of a honeycomb.

The extruded monolith may be dried by vacuum drying which includesplacing the extruded monolith in a vacuum chamber initially having roomambient temperature and atmospheric pressure within the vacuum chamber,reducing the pressure within the vacuum chamber at a rate and to a levelsufficient to freeze the water in the monolith, and maintaining thereduced pressure within the vacuum chamber for a time sufficient for thefrozen water to sublime until the monolith is dried. More particularly,the pressure within the vacuum chamber may be reduced, within about 1minute, from atmospheric pressure to a pressure less than about 1 torr,and desirably within the range from 30 microns to 1 torr.

The method of freeze drying the wet extruded monolith comprises thesteps of (1) freezing the water in the extruded monolith, (2) placingthe frozen extruded monolith in a vacuum chamber initially having apressure within the vacuum chamber of atmospheric pressure, (3) reducingthe pressure and/or temperature within the vacuum chamber at a rate andto a level sufficient to keep the water in the monolith frozen, and (4)maintaining the reduced pressure and/or temperature within the vacuumchamber for a time sufficient for the frozen water in the monolith tosublime until the monolith is dry. Desirably, during the freezing step,the water in the monolith is frozen within about 10 seconds to 10minutes after the extrusion step and the monolith is subjected to atemperature of less than about −25° F. More desirably, during thefreezing step, the monolith is subjected to a temperature of less thanabout −80° F.

The method of humidity control drying the wet extruded monolithcomprises the steps of (1) placing the extruded monolith in a chamberinitially having a relative humidity within the chamber of at least 95percent and (2) gradually reducing the relative humidity within thechamber until the monolith is dry.

This invention encompasses an adsorptive monolith made according to theforegoing process and a method of removing chemical agents such asvolatile organic compounds and ozone from a fluid air stream comprisingthe step of routing through the adsorptive monolith a fluid streaminitially including such a chemical agent.

The adsorptive monolith of this invention comprises ceramic material andactivated carbon dispersed throughout the matrix. The ceramic materialis reacted together such that a ceramic matrix is formed and theactivated carbon is supported by the matrix. The monolith desirably hasa plurality of passages therethrough to receive a flow of fluid and isin the shape of a honeycomb. In addition, the monolith desirably has anopen frontal area greater than 70% and up to 85% and an axial crushingstrength from about 500 to about 1600 psi.

Thus, an object of the present invention is to provide an improvedadsorptive monolith comprising activated carbon and an improved methodof making such a monolith.

Another object of the present invention is to provide an adsorptivemonolith for removing chemical agents such as volatile organic compoundsand ozone from fluid streams.

Yet another object of the present invention is to provide an adsorptivemonolith with desirable strength characteristics.

Still another object of the present invention is to provide improvedmethods of drying a wet extruded monolith comprising activated carbon,ceramic forming material, and water.

Other objects, features, and advantages of the invention will becomemore readily apparent from the following description of embodiments ofthe invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an adsorptive monolith made inaccordance with an embodiment of this invention.

FIG. 2 is a partial side elevation view of the monolith of FIG. 1 with aportion of the skin removed to illustrate the flow of fluid through thehoneycomb passages of the monolith.

FIG. 3 is a graph comparing the axial crushing strength of monolithsmade in accordance with embodiments of this invention with that ofmonoliths made without flux material.

FIG. 4 is a graph comparing the apparent density of monoliths made inaccordance with embodiments of this invention with that of monolithsmade without flux material.

DETAILED DESCRIPTION OF DRAWINGS

As summarized above, this invention encompasses an adsorptive monolithcomprising activated carbon, a method for making such a monolithincluding methods for drying the monolith, and methods for adsorbingchemical agents such as volatile organic compounds. As used herein,monolith means a block of solid-phase material. FIG. 1 illustrates amonolith 10 made according to an embodiment of the present invention.The monolith 10 shown in FIG. 1 is an extruded monolith comprisingactivated carbon and ceramic material and having a honeycomb shape. Themonolith has a plurality of passages 12 extending through the monolithfrom a frontal end 14 to a rearward end 16. The passages 12 aresubstantially square in cross section, linear along their length, andformed by surrounding walls 18 of the extruded material; however, thepassages can have other cross-sectional shapes such as rectangular,round, triangular, hexagonal, oval, eliptical, and the like. Thepassages 12 are encased by an outer skin 20 of the extruded material.

The monolith 10 is useful as an adsorptive filter to adsorb a variety ofchemicals from gaseous or liquid phases and as a catalyst substrate. Forexample, when the monolith 10 is disposed in the air intake system of afuel injected internal combustion engine, the activated carbon of themonolith adsorbs fuel vapors that escape from injector ports as fuelleakage when the engine is turned off. When the engine is restarted,incoming air sweeps back through the honeycomb structure and desorbs thefuel. The fuel is then combusted in the engine. FIG. 2 illustrates theflow of fluid through the passages 12 in the monolith 10. The materialto be adsorbed is adsorbed by the activated carbon held in the walls ofthe monolith structure.

In another example, the monolith 10 is positioned in the exhaust airstream of a xerographic device and the activated carbon of the honeycombstructure adsorbs ozone. The ozone is captured by the carbon, and iseither converted to oxygen (catalytically) or carbon dioxide (bychemical interaction with the carbon) or held captive long term byadsorption. More probably, combinations of the foregoing actually occur.In any case, the adsorptive monolith or filter removes ozone from theair stream, eliminating the discomfort and possible health hazard whichozone presents to the eyes and respiratory tissues of office workers inthe area.

Generally described, the monolith 10 is made by mixing togetheractivated carbon, ceramic forming material, flux material, binder, andwater to make an extrudable mixture. The extrudable mixture is extrudedthrough an extrusion die to form the monolith having the honeycombstructure. After extrusion, the extruded honeycomb monolith retains itsshape while it is dried and then fired at a temperature and for a timeperiod sufficient to react the ceramic forming materials to form amonolith having activated carbon dispersed throughout the structure andsufficient strength for its intended end use.

Desirably, the method for making the monolith 10 includes first mixingthe dry ingredients of the extrudable mixture and then adding the liquidingredients to the dry mixture; however, the order in which theingredients are added to the extrudable mixture can be varied byalternating mixing of dry and liquid ingredients as long as the properamount of moisture is added to make an extrudable mixture which holdsits shape during and after extrusion.

The activated carbon is desirably present in the extrudable mixture inan amount from about 20 to about 70 parts, by weight, and moredesirably, in an amount from about 30 to about 50 parts, by weight. Theactivated carbon adsorbs volatile organic compounds and other chemicalagents such as ozone. A variety of activated carbons can be used in thisinvention. The most suitable activated carbon will depend on theintended application, particularly the nature of the material to beadsorbed. Thus, the physical properties of the activated carbon, such asthe surface area and the pore structure, may vary depending on theapplication. Desirably, the activated carbon has a nitrogen B.E.T.surface from about 600 to about 2000 m²/g. More desirably, the activatedcarbon has a nitrogen B.E.T. surface from about 800 to about 1800 m²/g,and even more desirably has a nitrogen B.E.T. surface from about 1000 toabout 1600 m²/g. Suitable activated carbon can also be characterized byhaving a particle size such that more than 40% by weight of theactivated carbon passes through a 325 mesh screen, and more desirably,by having a particle size such that more than 65% by weight of theactivated carbon passes through a 325 mesh screen.

Activated carbon suitable for use in the present invention may be madefrom a variety of precursors including bituminous coal, lignite, peat,synthetic polymers, petroleum pitch, petroleum coke, coal tar pitch, andlignocellulosic materials. Suitable lignocellulosic materials includewood, wood dust, wood flour, sawdust, coconut shell, fruit pits, nutshell, and fruit stones. A particularly desirable commercially availableactivated carbon is NUCHAR® activated carbon available from WestvacoCorporation of New York, N.Y.

The ceramic forming material is present in the extrudable mixture in anamount from about 20 to about 60 parts, by weight, and more desirably,in an amount from about 30 to about 50 parts, by weight. The termceramic forming material means alumina/silicate-based material which,upon firing, is capable of reacting together to form a high strength,crystal/glass mixed-phase ceramic matrix. In this application, thereacted ceramic material provides a matrix for supporting the activatedcarbon and has sufficient strength to withstand handling and use of themonolith in the intended application and maintain its intended shapewithout cracking or otherwise disintegrating. The ceramic formingmaterial desirably includes a substantial portion of moldable materialwhich is plastic in nature and thus, when mixed with liquid, can bemolded or extruded into a shape and will maintain that shape throughdrying and firing. Such a suitable plastic or moldable material is ballclay. A particularly suitable commercially available ball clay is OLDMINE #4 ball clay available from Kentucky-Tennessee Clay Company ofMayfield, Ky. Other suitable plastic-like ceramic forming materialsinclude plastic kaolins, smectite clay minerals, bentonite, andcombinations thereof. Bentonite and smectites are desirably used incombination with ball clay or kaolin.

The ceramic forming material also desirably includes a filler materialwhich is non-plastic and reduces shrinkage of the monolith during thesteps of drying and firing. Such a suitable ceramic filler is calcinedkaolin clay. A particularly suitable commercially available calcinedkaolin clay is Glomax LL available from Georgia Kaolin Company, Inc. ofUnion, N.J. The filler desirably is present in the extrudable mixture inan amount up to about 15 parts, by weight, more desirably, from about 1to about 15 parts, by weight, and even more desirably, from about 3 toabout 10 parts, by weight. Other suitable filler materials includecalcined kyanite, mullite, cordierite, clay grog, silica, alumina, andother calcined or non-plastic refractory ceramic materials andcombinations thereof.

The flux material is present in the extrudable mixture in an amount fromabout 4 to about 20 parts, by weight, and aids in forming the ceramicbond between the ceramic forming materials by causing the ceramicforming material particles to react together and form a ceramic matrixat a lower firing temperature than if the flux material was not present.More desirably, the flux material is present in the extrudable mixturein an amount from about 4 to about 10 parts, by weight. Suitable fluxmaterials include feldspathic materials, particularly nepheline syeniteand feldspar, spodumene, soda, potash, sodium silicate, glass frits,other ceramic fluxes, and combinations thereof. A particularly desirablecommercially available flux material is MINEX® Nepheline Syeniteavailable from Unimin Specialty Materials, Inc. of Elco, Ill.

The wet binder is present in the extruded mixture in an amount fromabout 0.5 to about 5 percent, by weight, based on the solids content ofthe binder, and enhances the strength of the monolith after extrusion sothat the extruded monolith maintains its shape after extrusion andthrough drying and firing. The wet binder is desirably present in theextruded mixture in an amount from about 1 to about 3 percent, byweight, based on the solids content of the binder. A particularlysuitable wet binder is methylcellulose and a suitable commerciallyavailable methylcellulose is METHOCEL A4M methylcellulose available fromDow Chemical Company of Midland, Mich. Desirably, methylcellulose ispresent in the extrudable mixture in an amount from about 0.5 to about 5parts, by weight, of the extrudable mixture, and more desirably, fromabout 1 to about 3 parts, by weight. Another suitable binder, used incombination with methylcellulose, is an acrylic binder. Examples of suchpolymers are JONREZ D-2106 and JONREZ D-2104 available from WestvacoCorporation of New York, N.Y. and Duramax acrylic binder which isavailable from Rohm & Haas of Montgomeryville, Pa. The acrylic polymer,having a medium to high glass transition temperature, is desirablypresent in an amount up to about 4 parts, by weight, of the extrudablemixture, based on the solids content of the acrylic binder and moredesirably is present in an amount from about 1 to about 4 parts, byweight, of the extrudable mixture, based on the solids content of theacrylic binder. Other suitable binders include hydroxypropylmethylcellulose polymers, CMC, polyvinyl alcohol, and other temporarybinder/plasticizer additives.

Another desirable component of the extrudable mixture is sodium silicatewhich increases the strength of both the dry, but unfired monolith andthe fired monolith, and is a flux material. The sodium silicate is thusboth a binder when the monolith is in the dry state and a flux material,and is added to the extrudable mixture as a solution. The sodiumsilicate is desirably present in the extrudable mixture in an amount upto about 7 parts, by weight, based on the solids content of the sodiumsilicate, and more desirably in an amount from about 2 to about 7 parts,by weight, based on the solids content of the sodium silicate. Asuitable commercially available sodium silicate solution is a 40%solids, Type N solution, available from PQ Corporation, IndustrialChemicals Division, Valley Forge, Pa. Other suitable binders for thedried monolith include silica sol and alumina sol.

The extrudable mixture includes water in an amount sufficient to make anextrudable mixture and desirably includes from about 60 to about 130parts water, by weight. Preferably, the water is chilled before it isadded to the mixture and more preferably is added to the system at ornear 0° C. This low temperature helps keep the ingredients cool duringmixing, and helps to overcome any exotherm which may occur as a resultof mixing the ingredients, or as a result of heating of the mixture,which occurs as a result of the mechanical action of mixing.

The extrudable mixture is formed into a shape which will be the shape ofthe final monolith by passing the extrudable mixture through anextrusion die. The monolith has a block shape and includes at least onepassageway along its length and desirably includes a plurality ofpassageways extending along the length of the monolith. The monolith isdesigned to be placed in the stream of a fluid containing a material tobe adsorbed such that the fluid is forced through the passages in themonolith. Ideally, the amount of internal surface area of the monolithexposed to the fluid is maximized to maximize the efficiency of theadsorption. A honeycomb-shaped structure is preferred for the monolith.Honeycomb extruders are known in the art of ceramics and have been usedto produce ceramic monoliths.

Desirably, the honeycomb structure of the monolith 10 has an openfrontal area greater than 70 percent and up to about 85 percent, anddesirably about 73.8 percent, after drying and firing. The open frontalarea of the monolith is the percentage of open area of the monolithtaken across a plane substantially perpendicular to the length of themonolith. Furthermore, the monolith 10 desirably has a honeycomb patternwith square cells and about 540 cells per square inch. The honeycombstructure desirably has a cell-to-cell pitch of about 0.043 inches, acell wall thickness of about 6 mils, and an open frontal area of about0.0014 square inches per cell. More broadly, for a variety ofapplications, the cell density may vary from 1 to 800 cells per squareinch or higher, with the cell wall thickness ranging from about 150 milsto about 5 mils and the cell-to-cell pitch varying from about 1 to about0.035 inches.

The extruded honeycomb monolith 10 is dried in a manner so as to preventcracking of the structure. To alleviate cracking, the monolith is driedso that water is removed at substantially the same rate throughout themonolith. Preferred drying methods include vacuum drying, freeze dryingand humidity control drying. More conventional drying methods can beused to dry the monolith of the present invention but are less practicalcommercially. Such conventional methods include dielectric drying andwarm air drying with the monolith wrapped in plastic.

Vacuum drying of the extruded honeycomb monolith includes placing theextruded monolith in a vacuum chamber initially having ambient roomtemperature and atmospheric pressure within the vacuum chamber, reducingthe pressure within the vacuum chamber at a rate and to a levelsufficient to quickly freeze the water in the monolith, and maintaininga reduced pressure within the vacuum chamber for a time sufficient forthe frozen water in the monolith to sublime until the monolith is dried.This drying cycle may be interrupted temporarily to remove the monolithto another chamber after the monolith has been frozen. Freezing of thewater in the monolith immobilizes the water and stabilizes the size andshape of the monolith. The initial vacuum desirably is a deep vacuum toquickly and uniformly freeze the monolith. The vacuum freezes themonolith more uniformly than if the monolith were frozen in a coldchamber at atmospheric pressure. After freezing, the monolith may thenbe moved to a second chamber which does not require quite as deep avacuum as the first chamber. Sublimation can be completed in this secondchamber. Desirably, during vacuum drying, the pressure within the vacuumchamber is reduced, within about 1 minute, from atmospheric pressure toa pressure less than about 1 torr, and desirably within the range from30 microns to 1 torr. Alternatively, this second chamber can be atatmospheric pressure and sub-freezing temperature and the frozenmonolith can be dried with recirculating dehumidified air.

Freeze drying of the extruded honeycomb monolith is carried out in thesame manner as vacuum drying except that the structure is flash frozenbefore being placed into a vacuum chamber for drying by sublimation. Thewet monolith is frozen by placing the wet monolith in a super coldchamber cooled by liquid nitrogen or other means known by those skilledin the art. Desirably, the temperature of the chamber is −25° F. orlower, and more desirably −80° F. or lower, with a circulating air orgaseous environment. Alternatively, the monolith may be flooded with ordipped into super cold liquid such as liquid nitrogen to freeze themonolith.

During the drying stage of freeze drying or vacuum drying wherein themonolith is subjected to a vacuum, the temperature of the monolith maybe varied by application of energy by radiation, conduction, convection,or RF or microwave energy independently during drying to enhance waterremoval. Vacuum levels similar to those used for vacuum drying are used.The temperature of the monolith should be maintained at or below amaximum of 32° F. to avoid non-uniform water loss and cracking.

Humidity control drying of the wet extruded honeycomb monolith includesplacing the extruded wet monolith in a chamber initially having arelative humidity within the chamber of at least 92 percent andgradually reducing the relative humidity within the chamber until themonolith is dried. Desirably, the initial relative humidity level in thechamber should be 98 percent or higher. The humidity in the chamber canbe lowered in stages to effect substantially uniform moisture lossthroughout the monolith during each drying stage. The humidityconditioned air is circulated through the drying chamber and thepassages of the honeycomb monolith to ensure a uniform rate of moistureremoval throughout the monolith. The temperature within the chamber maybe varied to enhance the drying action.

After drying, the dried extruded honeycomb monolith is fired at atemperature from about 1600 to about 1900° F. and desirably from about1850 to about 1900° F., in a nitrogen or other non-oxidizing or slightlyreducing atmosphere. The monolith should be fired at a temperaturesufficient to react the ceramic forming materials together to create amatrix for holding the activated carbon and maintaining the honeycombshape of the extrusion. The bonds created by the firing should besufficient to create a matrix having a strength able to withstandhandling and use of the monolith in intended applications such as in anozone filter for a xerographic device, a fuel adsorber in an automobileair intake system, or a catalyst support. When used as a catalystsupport, the monolith of the present invention can be coated withconventional catalyst coatings using conventional coating methods. Therelatively high surface area of the material forming the monolith of thepresent invention makes it desirable as a catalyst support.

In a desired embodiment, the monolith is made by extruding a mixturecomprising: 30 parts, by weight, activated carbon; 50 parts, by weight,ball clay; 10 parts, by weight, calcined kaolin clay; 10 parts, byweight, nepheline syenite; 2.5 parts, by weight, methylcellulose; 2.8parts, by weight, sodium silicate solids; and 75 parts, by weight,water. The resulting honeycomb monolith has a high structural integrity,exhibiting axial crushing strength of about 1500 psi and a modulus ofrupture (MOR) of about 150 psi in the axial direction.

It should be understood that carbon-containing ceramic monoliths of thisinvention can be used in a variety of applications owing to the widerange of carbon content which the monoliths can contain. For example,monolith crushing strengths will vary depending on the relative amountsof carbon and ceramic forming material, the firing temperature, and theparticle size of the ingredients. In particular, a monolith for use asan automotive air intake VOC adsorption product demands a higherstrength and a carbon content from about 25 to about 35%, by weight,while a monolith for use as an ozone depleter demands a higher strengthand a carbon content from about 45 to about 60%, by weight. The axialcrushing strength for an automotive air intake VOC adsorption productcontaining 25% carbon, by weight, ranges from 1200 to 1600 psi and theaxial crushing strength for an ozone depleter containing 50% carbon, byweight, ranges from 500 to 1000 psi.

The following examples are designed to teach those of ordinary skill inthe art how to practice this invention:

EXAMPLE

Four formulations (A-D) of dry ingredients as shown in Table 1 were dryblended for about 4 minutes. An appropriate amount of water to make anextrudable mixture was added, and the ingredients wet mixed in a highenergy mixer for about 5 minutes until a mixture with acceptableextrusion properties was obtained.

TABLE 1 Formulation in parts by weight Ingredient A B C D activatedcarbon¹ 50 50 30 30 ball clay² 42 36 58 50 calcined kaolin³ 8 7 12 10nepheline syenite⁴ — 7 — 1 0 sodium silicate⁵ — 4.5 — 2.8 (solids fromaqueous solution) methyl cellulose⁶  3 3 2.5 2.5 water 83 102 66 75¹Available from Westvaco Corporation of New York, New York and having aBET surface area of 1500 m²/g and a particle size distribution such that65 to 85% are less than 325 mesh, 85 to 95% are less than 200 mesh, and95 to 100% are less than l00 mesh. ²Available from Kentucky & TennesseeClay Co. of Mayfield, Kentucky under the designafion OLD MINE #4 BallClay. ³Available from Georgia Kaolin of Union, New Jersey under thedesignation GLOMAX LL. ⁴Available from Umimin Specialty Materials ofElco, Illinois under the trademark MINEX ®. ⁵Available from PQCorporation, Industrial Chernicals Division of Valley Forge,Pennsylvania in solution form with 40% solids, Type N. ⁶Available fromDow Chemical Corporation of Midland, Missouri under the designation A4M.

The four mixtures were then individually extruded through honeycombextrusion dies to form wet molded honeycomb structures, wrapped inmultiple layers of plastic film to retard moisture loss, and dried in awarm air dryer at about 180 degrees F. for 24 hours.

When the monoliths were sufficiently dry, four samples were cut fromeach of the monoliths made from Formulations A-D. The samples were cutperpendicular to the direction of the monolith passages and had athickness of 12 mm. These samples were then fired to the temperaturesshown in Table 2 for a time period of one half to one hour in anelectric furnace purged with an inert atmosphere, and comparativeresults for axial crushing strength and apparent density weredetermined. These results are depicted in FIGS. 3 and 4, respectively.

TABLE 2 Firing Temperature (° F.) Formulation Sample 1 Sample 2 Sample 3Sample 4 A 1400 1600 1800 2000 B 1400 1600 1800 2000 C 1400 1600 18002000 D 1400 1600 1800 2000

FIG. 3 compares the axial crushing strengths of 200 cpsi monolithscontaining 30% activated carbon and 540 cpsi monoliths containing 50%activated carbon, both with and without nepheline syenite and sodiumsilicate as flux material. The axial crushing strength was measuredaccording to ASTM C695-91. It can be seen that Formulations C and Dcontaining 30% activated carbon display significantly higher axialcrushing strength than do Formulations A and B, which contain 50%activated carbon and correspondingly lower amounts of ceramic formingmaterials. Furthermore, it can be seen that the addition of fluxmaterial increases the strength of the monolith over monoliths whichhave the same amount of carbon and approximately the same amount ofceramic forming material and are fired at the same temperature.Specifically, FIG. 3 shows that the monolith of Formulation B, whichincluded 50 parts by weight carbon, and flux material, had superiorstrength than the monolith of Formulation A, which included 50 parts byweight carbon, and no flux material. Both the monolith of Formulation Aand the monolith of Formulation B were fired at the same temperature.Likewise, FIG. 3 shows similar results for the monoliths of FormulationsC and D. Formulation C included 30 parts by weight carbon, and no fluxmaterial, and Formulation D included 30 parts by weight carbon, and fluxmaterial. This results in the same strength potential for similarformulations when fired at lower processing temperatures with theincorporation of flux material.

FIG. 4 compares apparent density values of the samples from themonoliths made according to each of the formulations and fired at thevarious firing temperatures. The apparent density was measured accordingto ASTM C838-91 on samples having dimensions of 12 mm×12 mm×12 mm,regular parallelpiped cut to eliminate the monolith skin. Allformulations show an increase in apparent density with increase infiring temperature. This increase in apparent density results fromformation of ceramic structure from the ceramic forming materialspresent. FIG. 4 shows higher density in both formulations containing 30%activated carbon and correspondingly higher amounts of ceramic formingmaterials than the formulations containing 50% activated carbon. Also,particularly in Formulation D, the flux containing formulations displayan increase in apparent density over the formulations not containing theflux materials.

The foregoing description relates to embodiments of the presentinvention, and changes and modifications may be made therein withoutdeparting from the scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A honeycomb-shaped adsorptive monolith having aplurality of passages therethrough for receiving a flow of fluid, havingan open frontal area greater than 70% and up to 85%, and comprising afired ceramic material and activated carbon dispersed throughout theceramic material, the ceramic material forming a matrix and theactivated carbon being supported by the matrix, wherein the firedceramic material is comprised of ceramic forming material and afeldspathic mineral flux material and wherein the monolith has an axialcrushing strength from about 500 to about 1600 psi.
 2. An adsorptivemonolith as in claim 1 wherein the activated carbon is present in anamount from about 20 to about 70 parts by weight and the ceramicmaterial is present in an amount from about 20 to about 60 parts, byweight.
 3. An adsorptive monolith as in claim 1 wherein the activatedcarbon is derived from materials selected from the group consisting ofbituminous coal, lignite, peat, synthetic polymers, petroleum pitch,petroleum coke, coal tar pitch, and lignocellulosic materials.
 4. Anadsorptive monolith as in claim 1 wherein the activated carbon isderived from lignocellulosic materials selected from the groupconsisting of wood, wood dust, wood flour, sawdust, coconut shell, fruitpits, nut shell, and fruit stones.
 5. An adsorptive monolith as in claim1 wherein the activated carbon is characterized by a nitrogen B.E.T.surface area from about 600 to about 2000 m²/g.
 6. An adsorptivemonolith as in claim 1 wherein the activated carbon is characterized bya nitrogen B.E.T. surface area from about 800 to 1800 m²/g.
 7. Anadsorptive monolith as in claim 1 wherein the activated carbon ischaracterized by a nitrogen B.E.T. surface area from about 1000 to 1600m²/g.
 8. An adsorptive monolith as in claim 1 wherein the activatedcarbon is characterized by having a particle size such that more than40% by weight of the activated carbon passes through a 325 mesh screen.9. An adsorptive monolith as in claim 1 wherein the activated carbon ischaracterized by having a particle size such that more than 65% byweight of the activated carbon passes through a 325 mesh screen.
 10. Anadsorptive monolith as in claim 1 wherein the feldspathic mineral isnepheline syenite.
 11. An adsorptive monolith as in claim 1 wherein theflux material further comprises sodium silicate.
 12. An adsorptivemonolith as in claim 1 wherein the ceramic forming material is selectedfrom the group consisting of ball clay, plastic kaolins, smectite clayminerals, bentonite, and combinations thereof.
 13. An adsorptivemonolith as in claim 1 wherein the fired ceramic material furthercomprises a shrinkage reducing filler material.
 14. An adsorptivemonolith as in claim 13 wherein the shrinkage reducing filler materialis calcined kaolin clay.